<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    const sum = (...args) => {
      let total = 0;
      args.forEach((item) => {
        total += item;
      });
      // 等价于：args.forEach(item => total += item);
      return total;
    };
    console.log(sum(10, 20));     // 30
    console.log(sum(10, 20, 30)); // 60
  </script>
</body>
</html>